Continuous scaling of MOSFET results in smaller gate fill volumes for low resistivity metal (e.g., tungsten) deposition after formation of the metal gate stack. Suitable n-metal films have low work function (WF) thickness dependence and low resistivity. Additionally, the band edge work function performance should achieve both usable threshold voltage behavior and minimize short channel effects.
Existing n-metal TiAlC has high resistivity (>2000μΩ-cm) and requires ˜30 Å to achieve the useful work function for 10 nm devices. Thinning the TiAl film thickness to 20 Å and below leads to a significant increase in the effective WF. Further WF reduction is dependent on increasing Al concentration, which results in integration reliability and chamber defect challenges.
Therefore, there is a need in the art for integration schemes, gate stacks and new materials for work function scaling.